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Synthesis 2022; 54(04): 864-886
DOI: 10.1055/s-0040-1706052
DOI: 10.1055/s-0040-1706052
special topic
Cycloadditions – Established and Novel Trends – in Celebration of the 70th Anniversary of the Nobel Prize Awarded to Otto Diels and Kurt Alder
Allenes in Diels–Alder Cycloadditions
Australian Research Council (DP160104322)
Dedicated to the memory of Klaus Hafner
Abstract
For a long time, allenes—and cumulenic systems in general—played a relatively minor role in Diels–Alder cycloadditions. This situation has changed, since allenes are more readily available and as their unique stereochemical features in [4+2]cycloadditions are more widely recognized. This review presents a comprehensive overview of allenes in Diels–Alder processes using selected examples. Allenes in dienes, dienophiles and cycloadducts are covered, inter- and intramolecular Diels–Alder cycloadditions are discussed, and stereochemical features of the addition process are described. Areas of emerging importance are also covered, including allenic components in dehydro-Diels–Alder processes, and dendralenic allenes in Diels–Alder sequences for the rapid generation of target-relevant molecular complexity. Preparatively useful methods for allenic precursor synthesis are also discussed.
1 Introduction
2 Allenic Dienes
2.1 Vinylallenes
2.2 Bisallenes
2.3 Cross-conjugated Allenes
3 Allenic Dienophiles
4 Intramolecular Diels–Alder Cycloadditions
5 Allenic Cycloadducts
6 Conclusions and Outlook
Key words
Diels–Alder addition - allenes as dienes and dienophiles - intermolecular cycloaddition - intramolecular cycloaddition - stereoselective synthesis - dehydro-Diels–Alder reactions - rapid generation of molecular complexityPublication History
Received: 18 May 2021
Accepted after revision: 16 June 2021
Article published online:
04 August 2021
© 2021. Thieme. All rights reserved
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For related examples of this process in total synthesis, see:
These processes take place under thermal, photochemical, metal-induced, and base-catalyzed conditions. Thermal hexadehydro-Diels–Alder processes proceed through stepwise mechanisms: